What is the origin of Observables?

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Discussion Overview

The discussion revolves around the nature and origin of observables in quantum mechanics, specifically addressing why observables are typically represented by Hermitian operators, the implications of eigenstates and eigenvalues, and the conventions surrounding these definitions. The scope includes theoretical considerations and conceptual clarifications related to quantum mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question why observables must be Hermitian and whether this is by definition, suggesting that the convention may stem from historical or practical reasons.
  • Others argue that only Hermitian operators guarantee real eigenvalues, which aligns with the expectation that measured values must be real numbers.
  • A participant notes that the requirement for Hermitian operators is linked to the projections necessary for Born's rule, while also mentioning that non-Hermitian observables can exist in more general measurement frameworks.
  • Some contributions highlight that the mathematical formalism of quantum mechanics, including the use of Hermitian operators, is a result of historical developments and practical effectiveness rather than absolute necessity.
  • There is a discussion about the role of orthogonal states and the construction of observable operators from these states, with some participants suggesting that this is a convenient method for calculating averages.
  • One participant proposes that the use of Hermitian operators is related to their compatibility with the phenomenon of wave function collapse, while another counters that collapse does not necessarily occur to eigenstates.
  • Some participants introduce the concept of Positive Operator Valued Measures (POVMs) as a more general framework that extends beyond the traditional Hermitian operator approach.

Areas of Agreement / Disagreement

Participants express a range of views on the necessity and implications of using Hermitian operators for observables. There is no consensus on whether the conventions surrounding observables are fundamentally necessary or merely historical artifacts. Multiple competing perspectives on the nature of observables and their mathematical representation remain unresolved.

Contextual Notes

Participants acknowledge that the discussion involves assumptions about the mathematical framework of quantum mechanics, including the definitions of observables and the nature of measurement. The implications of these assumptions on the interpretation of quantum mechanics are not fully resolved.

  • #31
A. Neumaier said:
In a damped harmonic oscillator, the complex-valued frequency has a nonzero real and imaginary part.
A. Neumaier said:
The real observables are the points on the oscillating curve; the observable complex frequency is extracted from these and produces the physical way of summarizing the behavior of the oscillator.

It is always the summary that carries the physics. Without summarizing what happens in Nature we cannot form a single concept. Every observable is an abstraction of the real thing, and as an abstraction it may be a real number, a complex number, or an even more complicated object such as a vector or a tensor.
Nice post-editing :)

Sure, that's what I said, the real variable is a projection of the complex representation.

I am surprised that nobody else seems to be interested in whether the idea of complex observables makes sense physically. You and I are clearly not going to agree about that so we must agree to differ.
 
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  • #32
Derek Potter said:
I am surprised that nobody else seems to be interested in whether the idea of complex observables makes sense physically.
Take a wire and bend it to a sine wave :)
 

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